Electrical resistance device



May 9, 1944- c. A. FRAMBURG, JR, ErAL' 2,343,462

ELECTRICAL RESISTANCE DEVICE Filed July 16, 1942 &

llHIHIIl H1 //v VEN T0195 CD9 Fen/names J? E I4. LHRSON 0770 NEYPatented May 9, 1944 UNITED STATES PATENT OFFICE W. Larson, DownersGrove, 11L, assignors to Western Electric Company, Incorporated, NewYork, N. Y., a corporation of New York Application July 16, 1942, SerialNo. 451,154 16 Claims. (CL 201-75) This invention relates to electricalresistance devices and a method of making such devices and moreparticularly to a wound electrical resistance device and a method ofmanufacturing it.

It is an object of the present invention U provide a simple, inexpensiveand stable electrical resistance device and a method for expeditiouslyand economically making such devices.

In accordance with one embodiment of such an invention, a resistancedevice is formed by applying two layers of a polystyrene film to amandrel and, after winding several layers of the polystyrene filmon themandrel, a web or carbon or graphite coated or impregnated material,such as paper, may be interposed between the layers of film and aterminal element may be placed upon the carbon or graphite impregnatedmaterial. Continued rotation of the arbor will wrap the layers ormaterial about the arbor in a construction similar to that in woundcondensers and the layers or film will insulate the carbon or graphiteimpregnated material from adjoining layers of said material. After apredetermined number 01 layers of graphite impregnated material, havebeen wound on the arbor to provide the desired electrical raistancecharacteristics. a second terminal m y be placed on the coated materialand several more '0! 'film may be. made to.

complete the coil. After the coil thusbeenwound,alayerotscotchtapemaybeusedto hold thewrappings in place. The.rolled resist.- anceunitmaythenbesubiectedtoavacuum tor a predeterminedtimeat a relatively low. tern-- perature to remove. moisture. from theassembly and then without the-vacuumthe, temfbe. to apoint,whichverilire v lease the strains in the polystyrene fllm andcause it to shrink imiiormly thereby eirectively close the ends 01 therolled assembly against the entranceoi moisture, The resistance unitthus. formed may be used in this conditioner, it desired, may be pottedand coveredwith a moisture I resistantcompotmd it so desired.

In another 01-. the invention a p e rality or narrow, strips 01 per maybe wound between layers of polystyrene film which wide. enough to cover.the strips when the strips arespeced apart. and interconnected byconducting connector members to pro-- vide a resistor having a largeamount of resistance.

a better understanding of the invention will be had by reference to theaccompanying drawing, wherein V Fig. lisaviewinperspectiveoi'amandrelhavingtwo layers of polystyrene film attached thereto by means of astrip of scotch tape and showing the relative position oi. the layers ofpolystyrene film and graphite or coated carbon material, together withthe position of the terminals whereby the electrical connections may bemade to the carbon or graphite coated material; Fig. 2 is a view inperspective of the resistance unit after it has been rolled on themandrel, after it has the terminals assembled with it and. prior toheating it at a relatively high temperature;

Fig. 3 is a perspective view of the completed resistance unit after ithas been subjected to a temperature such that the strains in the poly-15 styrene film will be released.

Fig. i is a fragmentary sectional, view taken through the end portion ofthe wrappings of film and coated or impregnated material, as shown inFig. 3, and

Fig. 5 is a fragmentary developed view or an alternate arrangement ofimpregnated paper strips and terminals.

Referring to the drawing, wherein like reference numerals designate thesame parts throughout the several views, a mandrel iii, in the form of acopper tube, may be placed in any suitable winding apparatus, forexample, a condenser winding machine, and after the mandrel has beenplaced in the machine, two layers 0t 30 polystyrene film ll --il may beattached. to the mandrel by means of a piece 01' scotch tapell and themandrel rotated several turns to apply insulating layers, ofpolystyrene; iilrnv on the man- After the layers of, filmhave been thuswound on the mandrel, a layeroi graphite or carbon or impregnatedmaterial, for example, agraphite impregnated paper It, maybe insertedbetween thelayers oi film Ii wrapped on the arbor lland' a terminal inthe form of a metallic connector member i4, maythen be placed upon thelayer of graphite impregnated paper. Aiter the impregnated paper l3 andthe terminal ll have been placed inthe approximateposition shown in 1,the mandrel .tlmay be rotated to wraps number oi'layersot graphite.impregnated paperinto aunityasfshownin Fig, 2. suiiicient graphiteimpregnated paper has, been wound into the unit, to provide; thederesistance characteristics. a second terminal- I5 may beplaced onti'iegraphite impregnated paper andthe mandrel rotatedv a sufficient toprovide overlapping edges of polystyrene film li-li extending beyond theend of the impregnated paper llto insulate the endo! the'resistancematerial from contact with outside metallic parts and thereupon anotherlayer of scotch tape l may be used to hold the layers of polystyrenefilm in the position as shown in Fig. 2.

scription hereinbeiore has been of the construction of resistanceelements as shown in Figs. 1, 2, 3 and- 4, an alternate arrangement ofthe parts making up the resistance device may be made,

After a number of wrappings of graphite or 5 as shown in Fig. 5. In thisfigure, layers of carbon impregnated paper have been wound in plasticfilm 20 may be assembled with strips 2|, the manner just described, andinsulated one 22, 23 and 24 of carbon or graphite impregnated fromanother by the layers of polystyrene film Paper po t Shown in 5 and witha with the terminals l4 and I5 extending beyond metallic connector 25interconnecting the right the edgesof the polystyrene film to providecon- 10 ends of the strips 22 and 23 and with terminals nectingelements, the assemblage may be sub- 26 and 21 engaging the right endsof the strips jected to a temperature of approximately 120 F. 2| and 24.In addition to these connectors and for approximately hours while avacuum of terminals, a pair of terminals 28 and 29 may be approximatelyfour millimeters of mercury is approvided for interconnecting the leftends or the plied thereto in order to remove any trace of is strips 2|and 22 and the left ends of the strips moisture from between the wrappedlayers of 23 and 24, respectively. With this arrangement graphiteimpregnated paper and polystyrene film. of strips of carbon or graphiteimpregnated Ai'ter the assembly has thus been dried, the tem- I materialand terminals and connectors insulated perature may be raised slowly toapproximately by layers of plastic film and wound on a mand 130 n e a 2F. go drel, the single resistance unit of relatively smallThepolystyrene film utilized herein is the size may be connected invarious electrical cirusual commercial product which is sold in a cuitsto provide four diflerent resistance values; condition whereit isstretched 100% and when for example, if the terminals 2'! and 28 areused the temperature of this film is raised to apto connect theresistance device in a circuit proximately 195 F., the strains in thepoly- 25 only, the strip 24 of carbon impregnated matestyrene film willbe released and shrinkage will rial will be connected in the circuit. 11the ensue, whereby the polystyrene film will tend terminals 28 and 29are connected in a circuit. to return to its unstretched condition. Inso the resistance provided will include only the doing, the layers ofresistance material comprisstrips of carbon or graphite impregnatedpaper ing a graphite impregnated web oi"paper II will 3 22 and 23. Ifthe terminals 21 and 28 are conbe appreciably comprmsed and the ends ofthe nected in the circuit, the resistance in the cirpolystyrene film,which, as maybe seen in the cult will be the sum of the resistance ofthe figures of the drawing, extend an apthree carbon or graphiteimpregnated strips 22. preclabl'e distance beyond the edges 0! the 23and 24, whereas it the terminals 26 and 21 mphite impregnated paper II,will shrink are connected in the circuit, all of the strips down ontothe mandrel ll andassume substan- 2|, 22, 23 and 24 of impregnatedmaterial will tially the position shown in Fig. 3, thereby to beconnected in the circuit. effectively seal the ends of the convolutionsof It has been found that when carbon or film against the mandrel andagainst each other. graphite impregnated paper is wound into a re- Thiswill prevent the entrance of any moisture 40 sistance unit in the mannerdescribed hereinbetween the convolutions or the wound resistbefore andsealed between layers of plastic film -ance element and provide anefiective seal. which have been shrunk by releasing the strains Inaddition to effectively scaling the ends of set up in them inmechanically working them, it the resistance unit against thepenetration of will result in the temperature coefilcient of suchmoisture, the comprossi ngteflect or the polyresistance units beingconsiderably improved in styrene film, in to its unstretched comparisonwith units wound without shrinking condition, will placethegraphiteinthe graphite of the plastic film, apparently because of theimpregnated :paperunder a definite pressure pressure applied to thelayers oi impregnated which will be maintained duetothe stability ofmaterial by the plastic film. the polystyrene film atmospheric What isclaimed is! conditions of temperature and humidity and 1. An electricalresistance device comprising a q the resistance unit thus formedwillmalntain its continuous web of material impregnated with acharacteristics under the temperaconducting material to form aresistance elel5 t, l llldiw to which it would normalLv meat, acontinuous web of insulating material be su lected wider and longer thanthe resistance element to 7.1 desired, the resistance unit thus formed,enclose the edges and ends of the resistance y; may be mounted by meansof the mandrel l0 element, andterrn'inals engaging the resistance or maybepotted in a manner similar to that element and extending beyond theedges '01 the inwhich condensers are potted, using any suitinsulatingmaterial." V, ablepotting compound and whether used in the w 2. Anelectrical resistance device comprising a l fi ate shown in Fig. 3, orpotted, the resistance continuous web 01 materialimpregnated with a igwill maintain its resistance characteristics conducting material to forma resistance; elederivaryingtemperature and moisture condiment, acontinuous web ot'insulating material tions-to which such a pieceo!apparatus may be wider and longer than the resistance element. $l b1$ d-55 said web of insulating material comprising a ,1. While the materialdescribed herelnbeiore film of plastic material which has been"shrunk ybeen referred to a. polystyrene film, it will by re-orientation otitsmolecules to enclose the i ,beunderstood that any of the plastic films,such edges and ends oi. the resistance element, and as longllnearstraight chain polymers and coterminals engaging j theresistance'element and po ymers or other long chain compounds such as 7extending beyond the edges of the insulatiml polyamides or polyesters,the molecules of which lnlbe oriented by mechanical working andthe I Iof which, under subsequent heating, devices whichcomprises-simultaneously winding their random position within the a weboi graphite impregnated-material and a iilm maylbe used Furthermore,while the deweb 01 aplastic film, the moleculesEoi which material. A

3. The method of forming electrical resistance have been oriented bymechanical working on a mandrel, and then releasing the strainsgenerated in the film by the working thereof tocausethefilmtoshrinkandsealtheimpregnated material from outsideatmosphere solely by said shrinking..

4. The method of forming an electrical resistance device which comprisesinterposing a layer of graphite impregnated paper between layers ofpolystyrene film, wrapping the film and impregnated material on amandrel with the film overlapping the ends and edges of the impregnatedmaterial, heating the assembly to release the strains in the polystyrenefilm and shrink it. to completely surround the impregnated material byshrinking the overlapping edges of the film into intimate contact onewith the other.

5. The method of forming electrical resistance devices which compriseswinding a relatively narrow strip of graphite impregnated paper and aweb of polystyrene film longer and wider than the strip of paper on amandrel, treating the assembled strips and web to remove moisture fromthem and slowly raising the temperature of the assembly to form 195 F.to not more than 205 F. to cause the polystyrene film to shrink .andseal its edges one to another solely by said shrinkage.

the edges of the impregnated material, applying a terminal to theimpregnated material adjacent the outer end thereof, overlapping theouter end of the impregnated material with an extension of the layer offilm, attaching the end of the film to the adjacent layer thereof, andthen treating the assembly to cause the molecules in the film to rmumetheir normal orientation,

thereby to shrink the edges of the film into intimate engagement witheach other for sealing the impregnated material from-contact with outaside atmosphere.

6. An electrical resistance unit comprising a web of graphiteimpregnated material and a web of an initially set pre-stretchedinsulating material wound in superposed layers and said initially setpre-stretclfled material being shrunken from its pre-stretched conditionafter being assembled with the graphite impregnated material.

'7. An electrical resistance unit comprising webs of graphiteimpregnated material and prestretched insulating material wound insuperposed layers, said web of insulating material being wider andlonger than the graphite impregnated material and being shrunken fromits pro-stretched condition to completely enclose the graphiteimpregnated material.

11. A method of .formingan electrical resistance device which compriseswrapping upon a mandrel a layer of a web of plastic material which hasbeen pre-stretched by disturbing the normal orientation of itsmolecules, applying a web of graphite impregnated material to the layerof film on the mandrel, wrapping the film and impregnated material aboutthe mandrel to wind superposed layers of film and impregnated materialin a wrapped condition about the inandrel, inserting a terminal elementagainst the surface of the impregnated material with its end extendingbeyond the edge of the film, said film being wrapped with its edgesextending beyond the edges of the impregnated material, applying aterminal to the impregnated material adjacent the outer end thereof,overlapping the outer end of the impregnated material with an extensionof the layer of film, attaching the end of the film to the adjacentlayer thereof, subjecting the assembly thus formed to a temperaturewhich will cause the'molecules in the film to attempt to resume theirnormal orientation, thereby to shrink the edges of the film intointimate contact one with another and to compress the layers ofimpregnated material between the layers of film.

12. A method of forming an electrical resistance device which compriseswrapping upon a mandrel, a layer of a web of plastic material which hasbeen pre-stretched by disturbing the normal orientation of itsmolecules, applying a 8. In an electrical resistancedevice, a web of webof graphite impregnated material to the lay graphite impregnatedmaterial interposed between layers of a web of insulating material woundin a stretched condition with the impregnated material and shrunken toseal the edges of the layers of conducting material within theinsulating material. a

9. I an electrical resistance device, a web of carbon impregnated paperinterposed between layers of a web of plastic film, the molecules of erof film on the mandrel, wrapping the film and impregnated material aboutthe mandrel to wind superposed layers. of film and impregnated materialin a wrapped condition about the mandrel, inserting a terminal elementagainst the surface of the impregnated material with its end extendingbeyond the edge of the film, said film being wrapped with its edgesextending beyond the edges of the impregnated material, applywhich havebeen oriented by working and caused as mg a terminal to the impregnatedmaterial adto resume their random position under subsequent heating toshrink the overlapping edges oi. the film intointimatecontact withadjacent layers of film and seal the edges of the layers of film to eachother to enclose the impregnated a inserting a terminal element againstthe surface of the impregnated material with its end extending beyondthe edge of the film, said film being wrapped with its edges extendingbeyond jacent the outer end thereof, overlapping the outer end of theimpregnated material with an extension of the layer of film, attachingthe end of the film to the adjacent layer thereof, and sealing theimpregnated material from contact by surrounding atmosphere by treatingthe filmto cause its-molecules to attempt to resume their normalorientation.

13. A resistance unit comprising alternate layers of graphiteimpregnatedpaper, a polystyrene film wrapped on a mandrel with thepolystyrene film in a shrunken condition. after having been wound in astretched condition and with the edges of the polystyrene film extendingbeyond the edges of the impre nated paper so that on shrinking thepolystyrene film has sealed the impregnated paper from contact by thesurrounding atmosphere.

14. A resistance unit comprising alternate layers of graphiteimpregnated paper and a polystyrene illm wrapped on a mandrel with thepolystyrene iilm in a shrunken condition after having been wound in astretched condition and with theedges-ot the Polystyrene illrn extendingbeyond edges of the impregnated paper so that on shrinkingthepolystyrene film has sealed .the impregnated paper from contact bythe surrounding atmosphere. and a-plurality oi terminals engaged withthe impregnated paper and irictionally held in engagement therewith bythe shrunken layer 01' film.

.15. 'An electrical resistance 7 de ice, jwmnrising a continuous web ofa carbon impregnated material, a continuous web of an initiallysetprestretched insulating material wider and longer than the web of carbonimpregnated material. said webs being wound with the initially setprestretched material in its stretched condition and the web or carbonimpregnated material to extend beyond the ends and edges of the carbonimpregnated material and being shrunk to seal the edges of the carbonimpregnated material from the surrounding atmosphere solely by theshrinkage of the insulating material.

CHARLES A. FRAMBURG, JR. ELBERT W. LARSON.

